Packet loss about 3%, when pings pass between IPSec tunnel and physical port on 800C

[Kevex]

I've been trying to figure out why I'm losing about 3% of my pings across a new IPSec tunnel.  

Note: The pings are 100 bytes, with 1000 ms timeout.  The remote Fortigate's port 4 is the gateway for the LAN at the remote site.

Here's what I've found.

[ul]

When I ping across the IPSec VPN to anything on the remote LAN, I have about 3% packet loss.

When I ping across the IPSec VPN to the Fortigate's IP address on the LAN interface, there is zero packet loss.

When I ping from the Fortigate's LAN interface to anything on the LAN, there is zero packet loss.[/ul]

The 800C is running version 5.2.4 (yes, I know it's old. corporate bureaucracy) 

CPU utilization is under 10% on all four CPUs.

GF-FG800C-1 (root) # fnsysctl ifconfig port4 port4 Link encap:Ethernet HWaddr xx:xx:xx:xx:xx:xx:xx inet addr:10.4.32.18 Bcast:10.4.32.31 Mask:255.255.255.240 UP BROADCAST RUNNING PROMISC ALLMULTI MULTICAST MTU:1500 Metric:1 RX packets:5245303741 errors:0 dropped:0 overruns:0 frame:0 TX packets:8058790619 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:100 RX bytes:1554562707785 (1447.8 GB) TX bytes:8758638824464 (8157.1 GB)

I welcome anyone's input, as long as it doesn't start with, "I don't know anything about that, but..." 

Thank you.